Question

Assertion :On stimulation, a muscle cell releases calcium ions ($C{a}^{2+}$) from sarcoplasmic reticulum. Reason: By reacting with a protein complex, $C{a}^{2+}$ uncover active sites on the actin filaments.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

A neural signal on reaching the neurotransmitter junction releases acetylcholine, hence generating an action potential in the sarcolemma. As this potential spreads across the muscle fibre, releasing Ca${}^{2+}$ from the sarcoplasmic reticulum to the sarcoplasm. The increase in Ca${}^{2+}$ levels, binds it to troponin on the actin and hence unmasks active sites for myosin.

Therefore, the correct reason for the release of calcium ions from sarcoplasmic reticulum is action potential from the sarcolemma.